1. Technical Field
The present disclosure relates to fluid chambers for microfluidic and micromechanical applications, and more particularly, to formation of fluid chambers with particular dimensions.
2. Description of the Related Art
In applications using microfluidic structures or micro-electro mechanical structures (MEMS), fluid is often held in a chamber where it is heated. The most common application is inkjet printer heads. Other applications include analyzing enzymes and proteins, biological examinations, and amplifying DNA. Some of these applications require processing fluids at specific temperatures and require accurate regulation.
For example, a DNA amplification process (PCR, i.e., Polymerase Chain Reaction) requires accurate temperature control, including repeated specific thermal cycles. Often, only very small amounts of fluid are used, either because of a small sample or the expense of the fluid. Reliable and predictable chamber shapes are important to accurately heat the liquid in the chambers.
Inkjet technology relies on placing a small amount of ink within an ink chamber, rapidly heating the ink, and ejecting it to provide an ink drop at a selected location on an adjacent surface, such as a sheet of paper. Currently, formation of the ink chamber includes forming a sacrificial oxide on a wafer, forming heater components, and forming a nozzle opening. The sacrificial oxide is approximately one micron thick and 200 microns wide. After formation of these components, a first potassium hydroxide (KOH) etch forms a manifold in a backside of the wafer. Subsequently, the sacrificial oxide is removed by a hydrogen fluoride (HF) etch. Then a second KOH etch is used to enlarge the cavity to form the desired ink chamber to the desired size.
The final size of the chamber is not precise due to the imperfections of the second KOH etch. The chamber profile relies completely on the second KOH etch. To get uniform etch inside the whole cavity requires a very stringent process control, i.e., a long etch time at a stable temperature and chemical concentration. In addition, during the second KOH etch, a fresh chemical supply and exchange of by products are passed through the opening of the manifold from the backside. In order to have good chemical transport, the opening must be large enough, i.e., approximately 1000 microns in diameter. This large size causes the wafer to be porous and fragile, which makes it difficult to handle.
It is critical to know the size and profile of the chamber in order to optimize performance of the structure. Currently, there is no available inline method to inspect and measure the chamber size and profile.